Black Holes May Have Been Common in Early Universe

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Black holes may have been abundant among the first stars in the
universe, helping explain the origin of the supermassive monsters
that lurk at the heart of galaxies today, researchers say.

An international team of astronomers has found that
black holes likely contributed at least 20 percent of the
infrared cosmic background, light emitted 400 million to 800
million years after the Big Bang that created our universe 13.8
billion years ago.

"It's a relief to find a possible signature of these seeds,"
study co-author Guenther Hasinger, director of the Institute for
Astronomy at the University of Hawaii in Honolulu, told
SPACE.com.

The earliest black holes

Black holes possess gravitational fields so powerful that not
even light can escape. They are generally believed to form after
a star dies in a gigantic explosion known as a supernova, which
crushes the remaining core into a tiny but incredibly dense
volume.

It's unclear how black holes grow to supermassive proportions,
but they can apparently do so quite rapidly. For example, some of
them were apparently already well-established by 800 million
years or so after the
Big Bang.

To learn more about the earliest stars and the first black holes,
the study team analyzed X-ray and infrared signals using NASA's
Chandra X-ray Observatory and Spitzer Space Telescope,
respectively.

The X-rays that Chandra saw likely came from matter that became
superheated as it rushed into black holes, researchers said. The
infrared rays Spitzer detected, on the other hand, make up the
cosmic infrared background, the collective light from clusters of
massive stars in the universe's first stellar generations after
the Big Bang, as well as from black holes, which generate vast
amounts of energy as they devour gas.

The investigators focused on a region known as the Extended Groth
Strip, a well-analyzed slice of sky slightly larger than the full
moon in the constellation Bootes. They concentrated on spots that
shone powerfully in both infrared and X-ray light. Black holes
are the only plausible sources that can produce both forms of
light at the intensities they looked at, scientists said.

"This measurement took us some five years to complete and the
results came as a great surprise to us," lead author Nico
Cappelluti, an astronomer with the National Institute of
Astrophysics in Bologna, Italy, and the University of Maryland,
Baltimore County, said in a statement.

"Our results indicate black holes are responsible for at least 20
percent of the cosmic infrared background, which indicates
intense activity from black holes feeding on gas during the epoch
of the first stars," co- author Alexander Kashlinsky, of NASA's
Goddard Space Flight Center in Greenbelt, Md., said in a
statement.

How monsters grow

These early objects could help explain the origins of
supermassive black holes, researchers said, and also shed light
on another puzzle from the universe's youth — a stage known as
reionization.

During this era between about 150 million to 800 million years
after the
Big Bang, radiation ionized the neutrally charged hydrogen
pervading the universe to its constituent protons and electrons.

"It is currently thought generally, although not unanimously,
that stars were responsible for reionization," Kashlinsky told
SPACE.com. "Our result indicates that black holes were a
significant, potentially dominant, contributor to that process."

It remains uncertain how massive these early black holes were.
They could be mini- quasars
containing a few tens of thousands of solar masses, born from the
collapse of giant clouds of gas and dust. Or they could be
micro-quasars a few hundred solar masses large spawned from
massive dying stars.

Mini-quasars would be heavily obscured by clouds and thus likely
would not factor into reionization very much, while micro-quasars
could easily pump out enough radiation to make a key
contribution, Hasinger said.

The Euclid mission from the European Space Agency and the eROSITA
mission from Russia and Germany might be able to shed more light
on these early black holes. In addition, NASA's upcoming James
Webb Space Telescope might be able to see these objects
individually, confirming whether they are mini-quasars or
micro-quasars, Hasinger said.